Fix quasiquote flattening bug, decouple relations from evaluator

- Fix qq-expand in eval.sx: use concat+list instead of append to prevent
  nested lists from being flattened during quasiquote expansion
- Update append primitive to match spec ("if x is list, concatenate")
- Rebuild sx_ref.py with quasiquote fix
- Make relations.py self-contained: parse defrelation AST directly
  without depending on the evaluator (25/25 tests pass)
- Replace hand-written JSEmitter with js.sx self-hosting bootstrapper
- Guard server-only tests in test-eval.sx with runtime check

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/sx/ref/js.sx

@@ -124,6 +124,8 @@
   "eval-call" "evalCall"
   "is-render-expr?" "isRenderExpr"
   "render-expr" "renderExpr"
+  "render-active?" "renderActiveP"
+  "set-render-active!" "setRenderActiveB"
   "call-lambda" "callLambda"
   "call-component" "callComponent"
   "parse-keyword-args" "parseKeywordArgs"